The invention relates to a multiple-substance alloy for targets of cathode sputtering apparatus for the sputtering of gold coatings having non-gold alloy contents which have 0.5 to 10 weight-percent aluminum and also have copper.
A multiple-substance alloy of this kind is disclosed in German Federal Patent 31 42 541, to which U.S. patent No. 4,466,940 corresponds, in which the gold content is between 45 and 65 weight-percent with a predominant range between 57.5 and 59.5 weight-percent.
In standard gold colors, which are based on a gold content up to 65 weight-percent, a large amount of non-gold metals is necessarily present, especially copper which serves as a "reddener." The influence of the copper must consequently be counterbalanced by aluminum serving as a "whitener," so that the red content, expressing itself in the CIELAB unit a*, will not be too high. The following CIELAB units are typical of attractive gold alloys:
______________________________________ Luster/brilliance L* = 85 to 90 Redness a* = 0.5 to 3 Yellowness b* = 26 to 30. ______________________________________
A gold surface whose CIELAB units are within the ranges stated above, is considered in western Europe as standard gold color.
The CIELAB units given above are determined by a method of measurement which has become well established in recent years with producers of surface coatings, especially decorative coatings. It is a colorimetric method in which a beam of light from a standardized light source having quite specific spectral properties is directed at the object being measured, and the reflected light in the visible wavelength range is evaluated. The degree of brilliance can also be determined by a mathematical evaluation, such as for example the proportions of red and yellow color which determine the gold color hue. The bases of the method of measurement are described, for example, in R.M. German, M.M. Guzowsky and D.C. Wright in "Journal of Metals," March 1980, pages 20 ssq., and by the same authors in "Gold Bulletin," July 1980, pages 113 ff.
If one attempts to obtain a standard gold color hue defined by the above ranges, with one of the known target alloys, the copper content of the layer is made so high by the sputtering process that, in spite of the high aluminum content then needed for hue balancing, corrosion resistance will no longer be sufficient. Consequently, it is not possible to correctly establish the standard values and at the same time obtain the necessary corrosion resistance. In particular it is impossible to obtain a high luster, expressed in a high L* value, of at least L* =85.
DIN Standard 8238 gives gold alloys with units 1N to 4N and declares these units to be standard colors. In the conversion of these old color values to the more recently employed CIELAB units, it is found that the above CIELAB standard values can be obtained only with a silver content in the alloy amounting to between 1 and 10 percent by weight. Such alloys, however, again prove to be not resistant to corrosion or tarnishing.
The invention is therefore addressed to the problem of quantifying the components of a multiple substance alloy of the kind described above such that the above-given ranges of the CIELAB Standard values will be obtained, that the target will have good sputtering properties with regard to a high sputtering rate, a constant coating composition over long periods of sputtering, and repeatable coating properties, and at the same time will lead to good resistance to corrosion.
The solution of the stated problem is accomplished in accordance with the invention, in the multiple-substance alloy specified above, by the fact that the gold content is between 85 and 98 weight-percent, preferably between 90 and 98 weight-percent, and especially preferably between 94 and 97 percent by weight. The aluminum content is preferably between 0.5 and 5 percent by weight.
On account of the markedly higher gold content, advantageous gold layers are obtained having gold hues whose CIELAB values are within the above-stated ranges. The targets in question are distinguished by very good sputtering properties at high sputtering rates, and also the coating composition and the repeatability of the coating properties remains known over a long period of sputtering. It is to be noted that the target material is consumed during the sputtering and that the same sputtering rate cannot be expected of all alloy components, so that usually even an increasing separation is to be expected. Experience, however, has shown that these effects do not occur or do not occur to a marked extent in the alloy composition according to the invention.
The multiple-substance alloy according to the invention also has the advantage that, with the aluminum content which is peculiar to it, not only the required gold hue but also good corrosion resistance and resistance to wear have been achieved. Furthermore, the same target has been used in successive cycles of operation to coat numerous batches without any impairment of the repeatability of the composition of the coating.
The circumstances can also be further improved by adding additional alloy components to the alloys, at least one additional alloy component being present, from a group of the metals Co, Ni, Ga, Ti, In, Cd, Sn, Fe and Pd with a content in each case of 0.1 to 5 weight-percent, the sum of all additional alloy components not exceeding the value of 6 weight-percent.
On account of the additional alloy components the copper content is, of course, further diminished. But in no case is the bottom limit or the top limit of the stated ranges always selected for each of the additional components. The selection of suitable values within the above-stated ranges can be determined by experiment.